Concrete over big rocks?


Need a bit of guidance here,

I have tough yard and my contractors are going to pour concrete over some large boulders and filled in the remaining area with parts of other boulders (6in to 1 foot). They are planning on using rebar but not much else. I have read this is not optimal but they are pretty deep into the project now - thoughts? Should I ask them to use extra rebar? Adjust the concrete mix so it is more liquid? Wet the rocks jut in advance of the pour so the concrete binds better. Any help you can provide is genuinely appreciated, a bit outside my comfort zone here.

q concrete over big rocks
  11 answers
  • Flipturn Flipturn on Jun 21, 2020

    'Just wondering why you may be doubting if the amount of rebar the contractors are using will be adequate, and so are thinking the project may need additional....... .

    What are you intending to do with the concrete area after it has cured?

    -Use it as a patio, store something heavy on it?

    Please tell us a little more about what the overall goal is here, so that we can try to assist you.

    • NotTooHandy NotTooHandy on Jun 21, 2020

      Thanks Flipturn - Going to put a 7 x 7 hot tub in lower left corner where fence line is - filled weight will be around 5000 lb. the rest will just be slab for patio chairs, etc. I was just wondering if given the base using more rebar would reduce the likely hood of slab problems. We live in southern California so frost is relatively rare.

  • Mogie Mogie on Jun 21, 2020

    We filled up the forms we used when we poured our stairs with broken bits of concrete and rocks. Saves on the amount of concrete used and didn't effect the strength of the stairs at all.

    If you are concerned why don't you just talk to your contractor. Perhaps their response will make you feel better.

    • See 1 previous
    • Mogie Mogie on Jun 21, 2020

      All different sizes. Some small like baseball and other so large it took two people to move them. Even used some old cement that was broken into chunks. That was over 20 years ago and there hasn't been a single problem.

  • Raise your concerns with the contractor, if they are a reputable company they would not take offense to you voicing your concerns.

    • See 2 previous
    • Oliva Oliva on Jun 22, 2020

      You have the right to make changes, but you may incur costs for a "change order". Nevertheless, I'd prefer the cost of a change order, to being unhappy for years to come with a bad job. Speak up! It's your money, your yard, your future view!

  • Chloe Crabtree Chloe Crabtree on Jun 21, 2020

    I would ask them to use rebar to reinforce the concrete.

    • NotTooHandy NotTooHandy on Jun 21, 2020

      Thanks Chloe! Yes, definitely, they have a ton of rebar set aside I am just wondering if having them use 2x as much as usual might help with cracking given the base material.

  • K. Rupp K. Rupp on Jun 21, 2020

    We poured a concrete patio in our yard and its holding up very well. Your's looks like it is on a slope like ours so did they talk about putting in a retaining wall or is this a sloping concrete pad? I will give you all of our posts because we diy'd everything so I have all the details from the beginning. Read up on it and compare so you can form your questions correctly:

    I have 3 posts associated with a patio on a slope where we prepared for the cement slab and We DIY'd the whole thing. I have ALL details in these posts starting it from scratch!!!

    1st post:

    -describes diagrams and sketches needed to build a retaining wall along with planning the wall and cement pad.

    -laid out how to plan and diagram a retaining wall.

    -math calculations to figure out how much stone and block to order

    -how far we dug down and the cross section diagrams of what is going on under the ground

    2nd post:

    -What we did to build the retaining wall.

    -what materials were needed.

    -the actual building pictures

    -preparation for the concrete pour

    3rd post:

    -how to order concrete

    -how much concrete we would need based on math calculations that I give you.

    -what materials we needed

    -the process of pouring the cement

    I hope this helps you, that is the exact reason why I wrote it! When you look at the posts, please feel free to comment with any questions. Good LUCK!!!

  • NotTooHandy NotTooHandy on Jun 21, 2020

    Thanks! we are building steps up to the concrete and will have the pad poured level. They are going to do the retaining wall in another portion of our property to help level the earth. Really in a tough spot as we have slopes all around our home :(

  • William William on Jun 21, 2020

    Seems like they are doing it right. Concrete will flow into crevices in between the boulders and rocks. The rebar will give the bonding strength to the concrete.

  • Kathy Gunter Law Kathy Gunter Law on Jun 22, 2020

    I would etch them first to help adhering, just like you would if they were pouring over existing concrete. Other than that, I think you will be fine.

  • Betsy Betsy on Jun 22, 2020

    Hi Not: I'd contact the city ordinance people and see what they think. I'm thinking you might have to get a permit for this and the ordinance, or whatever department covers this, will see that it's done right. And, don't you pull the permit, have the contractor do it. Never pull a permit unless you are doing the work, because that's what the permit is saying, that you are doing the work. If things go sideways and you pulled the permit, you won't have a leg to stand on. So, this looks like a job not to be taken lightly. Good luck

  • Rymea Rymea on Jun 23, 2020

    I'm assuming they know about the 5000lb hot tub. The question would be are they guaranteeing the slab against cracking and for how long. If it's guaranteed against cracking with "normal use" that might not include the extra weight of the hot tub. Get it in writing including what they will do in case the slab fails.

  • Agnes Chrzanowska Agnes Chrzanowska on Jun 30, 2020

    Rebars are really needed in this project

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